Many hospital patients, depending upon their medical condition, are confined to a bed within the institution to which they have been admitted. Confinement may be necessary for any number of reasons. Typically, a doctor might require such a course of action because of the administration of an intravenous solution, because the patient is too weak to be able to negotiate movement to, for example, the bathroom, etc.
Similarly, an admittee to a nursing home might also be confined to bed. Probably the most typical reason for confinement of the patient to bed in an institution of this nature is the weakness of the patient due to old age or infirmity.
Various types of apparatus have been devised to prevent a patient so confined from exiting his or her bed. Probably the most primitive of these apparatus are safety bars secured to the sides of the bed. Such devices, however, have significant restrictions upon the degree of success which can be achieved with their use. Although safety bars might be successful in certain instances in preventing falls from beds, even this is not always true. Because it is often necessary to transfer a patient from the bed into, for example, a wheelchair to transport the patient to another location in the institution, the bars are not continuous along the full length of the bed. If the patient happens to work himself or herself to a location on the bed at which the bars are not present, an inadvertent fall can still occur.
Even more significantly, however, safety bars are totally inadequate to ensure against a volitional vacation of the bed by the patient. If a patient, while lying in the bed, feels sufficiently strong to walk to, for example, the bathroom, he or she will likely be able to move to a discontinuity in the safety bars and exit the bed.
In order to guard against both inadvertent and volitional vacations of a patient from a bed, various types of devices have been constructed. One group of such structures deal with the problem by providing switches, pads, and circuit systems for monitoring at a remote location when a patient has vacated his or her bed. Typical of this type of device are the structures disclosed in U.S. Pat. Nos. Re.28,754 (Cook, et al); 4,172,216 (O'Shea); 4,179,692 (Vance); 4,195,287 (McCoy, et al); 4,228,426 (Roberts); 4,242,672 (Gault); 4,264,904 (McCoy); and 4,295,133 (Vance). The O'Shea patent, along with a number of the other references, teaches a way of monitoring wherein a number of sensing switches are provided. The structures of all of these references, however, merely sense whether a patient is on or off the bed. By the time the sensing has occurred and institutional personnel at a monitor station are alerted to the sensing of the patient being off the bed, the damage may well have already been done, the patient having fallen and injured himself or herself.
While the structures of the above-discussed patents are electrical or electronic in nature, various other devices have been constructed which effect sensing by other means. For example, the structure of U.S. Pat. No. 4,020,482 (Feldl) senses the presence or absence of a patient on a bed by measuring the air pressure in an elongated air inflated flexible bag which is positioned beneath the mattress on which the patient lies. The structure disclosed therein includes an alarm actuation switch which becomes actuated when the pressure in the bag drops below a pre-set actuation pressure. This structure, however, as with the structures of the above-discussed patents, merely detects presence or absence of the patient on the bed.
U.S. Pat. No. 4,245,651 (Frost) discloses an apparatus for detecting body movements on the surface of a bed. It provides an electro-mechanical transducer which has an aural emitter actuated by the compression or expansion of the device in response to movement of the patient, and a microphone for sensing the generated noise. The sensing of the generated noise can, in turn, under appropriate circumstances, initiate the actuation of an alarm. This structure, however, neither senses whether a patient is present or absent upon the bed nor whether he is approaching vacating the bed. Rather, it merely measures the amount of movement of the patient on the bed. In some cases, frequent and exaggerated movement can be indicative of an intent to vacate the bed, but this is not always true.
U.S. Pat. No. 3,961,201 (Rosenthal) illustrates a device similar in structure to the devices of the group of patents initially discussed. That patent teaches the presence of a mechanical switch proximate the edge of a bed which can sense the patient approaching the edge of the frame. When the patient's approaching the edge is sensed, an alarm becomes actuated. The structure of the Rosenthal patent does not, however, provide discrimination as to location of the patient on the bed, and, it would appear, the structure is incapable of being used at all locations about the bed through which the patient might escape.
U.S. Pat. No. 3,836,900 (Mansfield) discloses a mattress for detecting the movement or absence of movement of a patient thereon. The mattress includes resilient resistor material that is varyingly loaded as the patient moves so that changes in its electrical resistance occur giving rise to electrical output signal pulses that are monitored in a detector circuit. The device utilizes a number of layers of the resilient resistor material. The material may be a resilient plastic foam incorporating an electrically conductive material such as graphite, so that movement of one layer relative to a contiguous layer changes the contact resistance. These changes can, in turn, be detected by a suitable electrical circuit to actuate an alarm. As in the case of the structure of the Frost patent, the structure of this patent does not detect either the presence or absence of the patient on the bed or a condition in which the patient is approaching vacating the bed. Rather, it merely detects the volume of movement by the patient while he is on the bed.
U.S. Pat. No. 4,175,263 (Triplett, et al) discloses a structure which includes two sensors for determining the location of a patient on the bed. A first pressure sensing pad detects when the patient is in what the patent defines as a normal position. A second pressure sensor is positioned for sensing the weight of part of a patient's body when the patient moves into a position on the bed in a direction which would indicate an intent to vacate the bed. The structure of Triplett, however, precludes discrimination of location of the patient on the bed. Additionally, it assumes that the patient will attempt to vacate the bed by moving in one certain defined direction. That may or may not always be the case.
The present invention is an improved device which is capable of sensing whether a patient is either on or off the bed. More importantly, however, it can additionally sense where the patient is on the bed, whether the location of the patient is a "safe" location, and when the patient might move to vacate the bed. This is true regardless of the direction in which the patient might move in his attempt to exit from the bed. It is to all of the problems existent in the prior art, therefore, that the current invention is directed.